DOCSLIB.ORG

Top Quark and Heavy Vector Boson Associated Production at the Atlas Experiment

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Top Quark and Heavy Vector Boson Associated Production at the Atlas Experiment ! "#$ "%&'" (' ! ) #& *+ & , & -. / . , &0 , . &( 1, 23)!&4 . . . & & 56 & , "#7 #'6 . & #'6 & . , & . .3(& ( & 8 !10 92&4 . ) *)+ . : ./ *)#+ . *) +& . , & "#$ :;; &&;< = : ::: #>$ ? 4@!%$5%#$?>%'>'> 4@!%$5%#$?>%'>># ! #"?%# TOP QUARK AND HEAVY VECTOR BOSON ASSOCIATED PRODUCTION AT THE ATLAS EXPERIMENT Olga Bessidskaia Bylund Top quark and heavy vector boson associated production at the ATLAS experiment Modelling, measurements and effective field theory Olga Bessidskaia Bylund ©Olga Bessidskaia Bylund, Stockholm University 2017 ISBN print 978-91-7649-343-4 ISBN PDF 978-91-7649-344-1 Printed in Sweden by Universitetsservice US-AB, Stockholm 2017 Distributor: Department of Physics, Stockholm University Cover image by Henrik Åkerstedt Contents 1 Preface 5 1.1 Introduction ............................ 5 1.2Structureofthethesis...................... 5 1.3 Contributions of the author . ................. 6 2 Theory 8 2.1TheStandardModelandQuantumFieldTheory....... 8 2.1.1 Particle content of the Standard Model ........ 8 2.1.2 S-matrix expansion .................... 11 2.1.3 Cross sections ....................... 13 2.1.4 Renormalisability and gauge invariance ........ 15 2.1.5 Structure of the Lagrangian ............... 16 2.1.6 QED ............................ 17 2.1.7 QCD ............................ 18 2.1.8 Weak interactions .................... 20 2.1.9 Electroweak interactions ................. 22 2.1.10 Electroweak symmetry breaking ............ 22 2.2TestsoftheStandardModel................... 23 2.3 Questions not answered by the Standard Model ........ 24 2.4 Motivation for ttV¯ searches................... 25 2.5 The treatment of the Wt and tW Z processes with Diagram Removal.............................. 26 2.6EffectiveFieldTheory...................... 28 3 Experimental setup 32 3.1 The Large Hadron Collider ................... 32 3.2 The ATLAS experiment ..................... 33 3.2.1 Inner Detector ...................... 34 3.2.2 Liquid Argon Calorimeter ................ 36 3.2.3 The Tile Calorimeter . ................. 37 3.2.4 Muon system ....................... 39 3.2.5 Magnet system ...................... 41 3.2.6 Trigger system ...................... 41 4 Measurements of the ttV¯ production cross sections 43 4.1 Object definitions . ....................... 44 4.1.1 Jets ............................ 44 4.1.2 Electrons ......................... 45 4.1.3 Muons ........................... 46 4.1.4 B-jets ........................... 46 4.1.5 Missing ET ........................ 47 4.1.6 Overlap removal ..................... 47 1 4.2 Signal regions ........................... 47 4.3 Control regions .......................... 51 4.4 Fake leptons, overview ...................... 51 4.5 Background estimation with Diagram Removal ........ 53 −1 4.6 Analysis I at 8 TeV, 20.3fb .................. 58 4.6.1 Event yields I ....................... 58 4.6.2 The WZ background I .................. 59 4.6.3 Results I .......................... 59 −1 4.7 Analysis II at 13 TeV, 3.2fb ................. 62 4.7.1 Yields II .......................... 62 4.7.2 WZ II ........................... 62 4.7.3 Results II ......................... 62 4.8 Analysis III at 13 TeV, 36 fb−1 ................. 66 4.8.1 Yields III . ....................... 66 4.8.2 Redefinition of trilepton regions for analysis III .... 68 4.8.3 The WZ background III ................. 71 4.8.4 Fake leptons III ...................... 72 4.8.5 Results III ......................... 75 5 Effective field theory 77 5.1 Cross section and distributions with effective operators .... 77 5.2 EFT limits, simultaneous fit ................... 85 5.3 EFT simulations for ATLAS ................... 88 5.4 EFT limits from the 13 TeV measurement ........... 94 6 Conclusions and outlook 96 6.1 Uncorrelated systematic uncertainties .............107 6.2 Correlated systematic uncertainties . ..............107 7 Sammanfattning 109 2 Acknowledgements I would like to thank my supervisor Jörgen Sjölin for helping me choose the subject and to find my niches in the field, which have been more to the phenomenological side. I am grateful to my co-supervisor Sten Hellman and my team leader David Milstead for their feedback and support in the writing of this thesis. I am happy to be part of a supportive and positive group in Stockholm. Katarina in particular has been a rock. Many thanks to the colleagues and friends who helped proof read sections of my thesis. All the publications that this thesis is based on are the result of collab- orative work. In this thesis I highlight my contributions while also giving the overall context and results. Below, I acknowledge the contribution of my collaborators in the cases where we were working on closely related subjects. Hovhannes Khandanyan (Stockholm) developed the software and defined the signal regions of the trilepton channel that were used for the ttV¯ analysis I. I evaluated the systematic uncertainty on the WZ background for analysis I together with Kerim Suruliz (Sussex) and Jörgen Sjölin. Kerim provided the simulations in Sherpa, which I used to compute transfer factors and the largest extrapolation uncertainties for the WZ process for analysis I. For the ttV¯ analyses II and III, the WZ extrapolation uncertainties were evaluated by Kerim; I cite these results for completeness. The fake rates for analysis II and III were derived by Jörgen Sjölin. I was involved in the validation of the fake rates for analysis III. The final results for the ttV¯ analyses that are shown in this thesis were obtained by Tamara Vasquez Schroeder in analysis I and by Maria Moreno Llacer (CERN) for analysis II. Maria also redefined the regions in the same sign dilepton channel for analysis III, which gave us a higher expected sen- sitivity for the ttW¯ measurement. The fake factors used to scale the γ +X background for analysis III were derived by Alexandra Schulte (Mainz). I would like to thank Kerim for demonstrating the functionality of the software for analysis III, which allowed me to design the fit for the EFT coefficients in a nice way. Many thanks to Karl Gellerstedt (Stockholm) for dressing the ttl¯ +l− EFT samples so that I could derive the parameters for the EFT fit for analysis III in regions that closely resemble the signal regions of our analysis. I am grateful to Fabio Maltoni (UCLouvain) who welcomed me to his team and to the MCnet studentship program, which allowed me to spend three and a half months in Belgium, learning about Effective Field Theory and the Diagram Removal methods. For the EFT phenomenological analysis that I performed when I was based in Louvain, I worked together with Ioan- nis Tsinikos on simulating the ttμ¯ +μ− process. We discussed the strategy together with my supervisor for the time Fabio Maltoni and collaborators Eleni Vryonidou and Cen Zhang. Cen had provided the code describing 3 the top quark interactions in the framework of Effective Field Theory and patiently answered my questions that arose while I was working on he EFT fit for analysis III. I learned the Diagram Removal 2 method from Federico Demartin (UCLouvain) and had many discussions with him. On a more personal level, I would like to thank Ioannis for being my gym buddy and Joze for cooking for me while I was in Belgium, you made my stay more enjoyable. Thank you to my figure skating coach Susanne and skating friends Natasja and Camilla for the mental training and a great summer. Thank you to Henrik Åkerstedt for the photos with the ATLAS detectors and for many memorable adventures. I am very grateful for my big loving family and happy to have great friends. Thank you for helping me through the tougher periods and for lifting me up higher in good times. An extra high five goes to Ea, Mike, Lotta, Mariana, Surre, Tomas K. and Stefan. To my husband Tomas, you have been incredible. 4 1 Preface 1.1 Introduction The Standard Model (SM) of particle physics [1], [2] describes our best understanding of particle physics at present. The predictions of the Standard Model have been confirmed by the discoveries of the particles it predicts and by measuring their interactions. Some notable examples of this are the confirmation of electroweak unification by the discoveries of the W and Z bosons 1982 and 1983 [3] and the discovery of the sixth and heaviest quark, namely the top quark, by the CDF and D0 experiments at the Tevatron in 1995 [4]. In order to produce the heaviest particles of the SM and to study their properties, large energies are required. For this purpose, proton beams are accelerated to close to the speed of light inside the Large Hadron Collider (LHC) [5] and brought to collide at the centre of the ATLAS experiment [6]. The protons scatter against each other, creating new particles, which are registered in the ATLAS detector and then the collision events are analysed. In this thesis, the physics of top quarks is explored. The LHC acts as a top quark factory, producing millions of top quark pairs each year. The main focus of this thesis is on the production of top quark pairs in association with a vector boson (Z or W ) at the ATLAS experiment. In order to model an important background to ttZ¯ , namely single top associated tW Z production, at next-to-leading order in QCD, the resulting overlap with other processes needs
Load more

Recommended publications
  • The ATLAS Experiment
    The ATLAS Experiment Mapping the Secrets of the Universe Michael Barnett Physics Division July 2007 With help from: Joao Pequenao Paul Schaffner M. Barnett – July 2007 1 Large Hadron Collider CERN lab in Geneva Switzerland Protons will circulate in opposite directions and collide inside experimental areas 100 meters underground 17 miles around M. Barnett – July 2007 2 The ATLAS Experiment See animation M. Barnett – July 2007 3 Large Hadron Collider Numbers The fastest racetrack on the planet Trillions of protons will race around the 17-mile ring 11,000 times a second, traveling at 99.9999991% the speed of light. Seven times the energy of any previous accelerator. The emptiest space in the solar system Accelerating protons to almost the speed of light requires a vacuum as empty as interplanetary space. There is 10 times more atmosphere on the moon than there will be in the LHC. M. Barnett – July 2007 4 Large Hadron Collider Numbers The hottest spot in our galaxy Colliding protons will generate temperatures 100,000 times hotter than the sun (but in a minuscule space). Equivalent to a billionth of a second after the Big Bang M. Barnett – July 2007 5 LHC Exhibition at London Science Museum M. Barnett – July 2007 6 Large Hadron Collider Numbers The biggest most sophisticated detectors ever built Recording the debris from 600 million proton collisions per second requires building gargantuan devices that measure particles with 0.0004 inch precision. The most extensive computer system in the world Analyzing the data requires tens of thousands of computers around the world using the Grid.
    [Show full text]
  • Aaron Taylor Physics and Astronomy This
    Aaron Taylor Candidate Physics and Astronomy Department This dissertation is approved, and it is acceptable in quality and form for publication: Approved by the Dissertation Committee: Dr. Sally Seidel , Chairperson Dr. Pavel Reznicek Dr. Huaiyu Duan Dr. Douglas Fields Dr. Bruce Schumm CERN-THESIS-2017-006 04/11/2016 SEARCH FOR NEW PHYSICS PROCESSES WITH HEAVY QUARK SIGNATURES IN THE ATLAS EXPERIMENT by AARON TAYLOR B.A., Mathematics, University of California, Santa Cruz, 2011 M.S., Physics, University of New Mexico, 2014 DISSERTATION Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Physics The University of New Mexico Albuquerque, New Mexico May, 2017 ©2017, Aaron Taylor iii Acknowledgements I would like to thank Professor Sally Seidel, for her constant support and guidance in my research. I would also like to thank her for her patience in helping me to develop my technical writing and presentation skills; without her assistance, I would never have gained the skill I have in that field. I would like to thank Konstantin Toms, for his constant assistance with the ATLAS code, and for generally giving advice on how to handle data analysis. The Bs → 4μ analysis likely wouldn’t have gotten anywhere without him. I would like to deeply thank Pavel Reznicek, without whom I would never have gotten as great an understanding of ATLAS code as I currently have. It is no exaggeration to say that I would not have been half as successful as I have been without his constant patience and understanding. Thank you. Many thanks to Martin Hoeferkamp, who taught me much about instrumentation and physical measurements.
    [Show full text]
  • Triple Vector Boson Production at the LHC
    Triple Vector Boson Production at the LHC Dan Green Fermilab - CMS Dept. ([email protected]) Introduction The measurement of the interaction among vector bosons is crucial to understanding electroweak symmetry breaking. Indeed, data from LEP-II have already determined triple vector boson couplings and a first measurement of quartic couplings has been made [1]. It is important to explore what additional information can be supplied by future LHC experiments. One technique is to use “tag” jets to identify vector boson fusion processes leading to two vector bosons and two tag jets in the final state. [2] However, the necessity of two quarks simultaneously radiating a W boson means that the cross section is rather small. Another approach is to study the production of three vector bosons in the final state which are produced by the Drell- Yan mechanism. There is a clear tradeoff, in that valence-valence processes are not allowed, which limits the mass range which can be explored using this mechanism, although the cross sections are substantially larger than those for vector boson fusion. Triple Vector Boson Production A Z boson decaying into lepton pairs is required in the final state in order to allow for easy triggering at the LHC and to insure a clean sample of Z plus four jets. Possible final states are ZWW, ZWZ and ZZZ. Assuming that the second and third bosons are reconstructed from their decay into quark pairs, the W and Z will not be easily resolved given the achievable dijet mass resolution. Therefore, the final states of interest contain a Z which decays into leptons and four jets arising for the quark decays of the other two vector bosons.
    [Show full text]
  • Slides Lecture 1
    Advanced Topics in Particle Physics Probing the High Energy Frontier at the LHC Ulrich Husemann, Klaus Reygers, Ulrich Uwer University of Heidelberg Winter Semester 2009/2010 CERN = European Laboratory for Partice Physics the world’s largest particle physics laboratory, founded 1954 Historic name: “Conseil Européen pour la Recherche Nucléaire” Lake Geneva Proton-proton2500 employees, collider almost 10000 guest scientists from 85 nations Jura Mountains 8.5 km Accelerator complex Prévessin site (approx. 100 m underground) (France) Meyrin site (Switzerland) Probing the High Energy Frontier at the LHC, U Heidelberg, Winter Semester 09/10, Lecture 1 2 Large Hadron Collider: CMS Experiment: Proton-Proton and Multi Purpose Detector Lead-Lead Collisions LHCb Experiment: B Physics and CP Violation ALICE-Experiment: ATLAS Experiment: Heavy Ion Physics Multi Purpose Detector Probing the High Energy Frontier at the LHC, U Heidelberg, Winter Semester 09/10, Lecture 1 3 The Lecture “Probing the High Energy Frontier at the LHC” Large Hadron Collider (LHC) at CERN: premier address in experimental particle physics for the next 10+ years LHC restart this fall: first beam scheduled for mid-November LHC and Heidelberg Experimental groups from Heidelberg participate in three out of four large LHC experiments (ALICE, ATLAS, LHCb) Theory groups working on LHC physics → Cornerstone of physics research in Heidelberg → Lots of exciting opportunities for young people Probing the High Energy Frontier at the LHC, U Heidelberg, Winter Semester 09/10, Lecture 1 4 Scope
    [Show full text]
  • Arxiv:2001.07837V2 [Hep-Ex] 4 Jul 2020 Scale Funding Will Be Requested at Different Stages Across the Globe
    Brazilian Participation in the Next-Generation Collider Experiments W. L. Aldá Júniora C. A. Bernardesb D. De Jesus Damiãoa M. Donadellic D. E. Martinsd G. Gil da Silveirae;a C. Henself H. Malbouissona A. Massafferrif E. M. da Costaa C. Mora Herreraa I. Nastevad M. Rangeld P. Rebello Telesa T. R. F. P. Tomeib A. Vilela Pereiraa aDepartamento de Física Nuclear e Altas Energias, Universidade do Estado do Rio de Janeiro (UERJ), Rua São Francisco Xavier, 524, CEP 20550-900, Rio de Janeiro, Brazil bUniversidade Estadual Paulista (Unesp), Núcleo de Computação Científica Rua Dr. Bento Teobaldo Ferraz, 271, 01140-070, Sao Paulo, Brazil cInstituto de Física, Universidade de São Paulo (USP), Rua do Matão, 1371, CEP 05508-090, São Paulo, Brazil dUniversidade Federal do Rio de Janeiro (UFRJ), Instituto de Física, Caixa Postal 68528, 21941-972 Rio de Janeiro, Brazil eInstituto de Física, Universidade Federal do Rio Grande do Sul , Av. Bento Gonçalves, 9550, CEP 91501-970, Caixa Postal 15051, Porto Alegre, Brazil f Centro Brasileiro de Pesquisas Físicas (CBPF), Rua Dr. Xavier Sigaud, 150, CEP 22290-180 Rio de Janeiro, RJ, Brazil E-mail: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Abstract: This proposal concerns the participation of the Brazilian High-Energy Physics community in the next-generation collider experiments.
    [Show full text]
  • Arxiv:2003.07868V3 [Hep-Ph] 21 Jul 2020 Ejmnc Allanach, C
    CERN-LPCC-2020-001, FERMILAB-FN-1098-CMS-T, Imperial/HEP/2020/RIF/01 Reinterpretation of LHC Results for New Physics: Status and Recommendations after Run 2 We report on the status of efforts to improve the reinterpretation of searches and mea- surements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data. Waleed Abdallah,1, 2 Shehu AbdusSalam,3 Azar Ahmadov,4 Amine Ahriche,5, 6 Gaël Alguero,7 Benjamin C. Allanach,8, ∗ Jack Y. Araz,9 Alexandre Arbey,10, 11 Chiara Arina,12 Peter Athron,13 Emanuele Bagnaschi,14 Yang Bai,15 Michael J. Baker,16 Csaba Balazs,13 Daniele Barducci,17, 18 Philip Bechtle,19, ∗ Aoife Bharucha,20 Andy Buckley,21, † Jonathan Butterworth,22, ∗ Haiying Cai,23 Claudio Campagnari,24 Cari Cesarotti,25 Marcin Chrzaszcz,26 Andrea Coccaro,27 Eric Conte,28, 29 Jonathan M. Cornell,30 Louie D. Corpe,22 Matthias Danninger,31 Luc Darmé,32 Aldo Deandrea,10 Nishita Desai,33, ∗ Barry Dillon,34 Caterina Doglioni,35 Matthew J. Dolan,16 Juhi Dutta,1, 36 John R. Ellis,37 Sebastian Ellis,38 Farida Fassi,39 Matthew Feickert,40 Nicolas Fernandez,40 Sylvain Fichet,41 Thomas Flacke,42 Benjamin Fuks,43, 44, ∗ Achim Geiser,45 Marie-Hélène Genest,7 Akshay Ghalsasi,46 Tomas Gonzalo,13 Mark Goodsell,43 Stefania Gori,46 Philippe Gras,47 Admir Greljo,11 Diego Guadagnoli,48 Sven Heinemeyer,49, 50, 51 Lukas A.
    [Show full text]
  • Vector Boson Scattering Processes: Status and Prospects
    Vector Boson Scattering Processes: Status and Prospects Diogo Buarque Franzosi (ed.)g,d, Michele Gallinaro (ed.)h, Richard Ruiz (ed.)i, Thea K. Aarrestadc, Mauro Chiesao, Antonio Costantinik, Ansgar Dennert, Stefan Dittmaierf, Flavia Cetorellil, Robert Frankent, Pietro Govonil, Tao Hanp, Ashutosh V. Kotwala, Jinmian Lir, Kristin Lohwasserq, Kenneth Longc, Yang Map, Luca Mantanik, Matteo Marchegianie, Mathieu Pellenf, Giovanni Pellicciolit, Karolos Potamianosn,Jurgen¨ Reuterb, Timo Schmidtt, Christopher Schwanm, Michał Szlepers, Rob Verheyenj, Keping Xiep, Rao Zhangr aDepartment of Physics, Duke University, Durham, NC 27708, USA bDeutsches Elektronen-Synchrotron (DESY) Theory Group, Notkestr. 85, D-22607 Hamburg, Germany cEuropean Organization for Nuclear Research (CERN) CH-1211 Geneva 23, Switzerland dDepartment of Physics, Chalmers University of Technology, Fysikgården 1, 41296 G¨oteborg, Sweden eSwiss Federal Institute of Technology (ETH) Z¨urich, Otto-Stern-Weg 5, 8093 Z¨urich, Switzerland fUniversit¨atFreiburg, Physikalisches Institut, Hermann-Herder-Straße 3, 79104 Freiburg, Germany gPhysics Department, University of Gothenburg, 41296 G¨oteborg, Sweden hLaborat´oriode Instrumenta¸c˜aoe F´ısicaExperimental de Part´ıculas(LIP), Lisbon, Av. Prof. Gama Pinto, 2 - 1649-003, Lisboa, Portugal iInstitute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego, Cracow 31-342, Poland jUniversity College London, Gower St, Bloomsbury, London WC1E 6BT, United Kingdom kCentre for Cosmology, Particle Physics and Phenomenology (CP3), Universit´eCatholique de Louvain, Chemin du Cyclotron, B-1348 Louvain la Neuve, Belgium lMilano - Bicocca University and INFN, Piazza della Scienza 3, Milano, Italy mTif Lab, Dipartimento di Fisica, Universit`adi Milano and INFN, Sezione di Milano, Via Celoria 16, 20133 Milano, Italy nDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK oDipartimento di Fisica, Universit`adi Pavia, Via A.
    [Show full text]
  • Basic Ideas of the Standard Model
    BASIC IDEAS OF THE STANDARD MODEL V.I. ZAKHAROV Randall Laboratory of Physics University of Michigan, Ann Arbor, Michigan 48109, USA Abstract This is a series of four lectures on the Standard Model. The role of conserved currents is emphasized. Both degeneracy of states and the Goldstone mode are discussed as realization of current conservation. Remarks on strongly interact- ing Higgs fields are included. No originality is intended and no references are given for this reason. These lectures can serve only as a material supplemental to standard textbooks. PRELIMINARIES Standard Model (SM) of electroweak interactions describes, as is well known, a huge amount of exper- imental data. Comparison with experiment is not, however, the aspect of the SM which is emphasized in present lectures. Rather we treat SM as a field theory and concentrate on basic ideas underlying this field theory. Th Standard Model describes interactions of fields of various spins and includes spin-1, spin-1/2 and spin-0 particles. Spin-1 particles are observed as gauge bosons of electroweak interactions. Spin- 1/2 particles are represented by quarks and leptons. And spin-0, or Higgs particles have not yet been observed although, as we shall discuss later, we can say that scalar particles are in fact longitudinal components of the vector bosons. Interaction of the vector bosons can be consistently described only if it is highly symmetrical, or universal. Moreover, from experiment we know that the corresponding couplings are weak and can be treated perturbatively. Interaction of spin-1/2 and spin-0 particles are fixed by theory to a much lesser degree and bring in many parameters of the SM.
    [Show full text]
  • Three Lectures on Meson Mixing and CKM Phenomenology
    Three Lectures on Meson Mixing and CKM phenomenology Ulrich Nierste Institut f¨ur Theoretische Teilchenphysik Universit¨at Karlsruhe Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany I give an introduction to the theory of meson-antimeson mixing, aiming at students who plan to work at a flavour physics experiment or intend to do associated theoretical studies. I derive the formulae for the time evolution of a neutral meson system and show how the mass and width differences among the neutral meson eigenstates and the CP phase in mixing are calculated in the Standard Model. Special emphasis is laid on CP violation, which is covered in detail for K−K mixing, Bd−Bd mixing and Bs−Bs mixing. I explain the constraints on the apex (ρ, η) of the unitarity triangle implied by ǫK ,∆MBd ,∆MBd /∆MBs and various mixing-induced CP asymmetries such as aCP(Bd → J/ψKshort)(t). The impact of a future measurement of CP violation in flavour-specific Bd decays is also shown. 1 First lecture: A big-brush picture 1.1 Mesons, quarks and box diagrams The neutral K, D, Bd and Bs mesons are the only hadrons which mix with their antiparticles. These meson states are flavour eigenstates and the corresponding antimesons K, D, Bd and Bs have opposite flavour quantum numbers: K sd, D cu, B bd, B bs, ∼ ∼ d ∼ s ∼ K sd, D cu, B bd, B bs, (1) ∼ ∼ d ∼ s ∼ Here for example “Bs bs” means that the Bs meson has the same flavour quantum numbers as the quark pair (b,s), i.e.∼ the beauty and strangeness quantum numbers are B = 1 and S = 1, respectively.
    [Show full text]
  • Phenomenology Lecture 6: Higgs
    Phenomenology Lecture 6: Higgs Daniel Maître IPPP, Durham Phenomenology - Daniel Maître The Higgs Mechanism ● Very schematic, you have seen/will see it in SM lectures ● The SM contains spin-1 gauge bosons and spin- 1/2 fermions. ● Massless fields ensure: – gauge invariance under SU(2)L × U(1)Y – renormalisability ● We could introduce mass terms “by hand” but this violates gauge invariance ● We add a complex doublet under SU(2) L Phenomenology - Daniel Maître Higgs Mechanism ● Couple it to the SM ● Add terms allowed by symmetry → potential ● We get a potential with infinitely many minima. ● If we expend around one of them we get – Vev which will give the mass to the fermions and massive gauge bosons – One radial and 3 circular modes – Circular modes become the longitudinal modes of the gauge bosons Phenomenology - Daniel Maître Higgs Mechanism ● From the new terms in the Lagrangian we get ● There are fixed relations between the mass and couplings to the Higgs scalar (the one component of it surviving) Phenomenology - Daniel Maître What if there is no Higgs boson? ● Consider W+W− → W+W− scattering. ● In the high energy limit ● So that we have Phenomenology - Daniel Maître Higgs mechanism ● This violate unitarity, so we need to do something ● If we add a scalar particle with coupling λ to the W ● We get a contribution ● Cancels the bad high energy behaviour if , i.e. the Higgs coupling. ● Repeat the argument for the Z boson and the fermions. Phenomenology - Daniel Maître Higgs mechanism ● Even if there was no Higgs boson we are forced to introduce a scalar interaction that couples to all particles proportional to their mass.
    [Show full text]
  • MIT at the Large Hadron Collider—Illuminating the High-Energy Frontier
    Mit at the large hadron collider—Illuminating the high-energy frontier 40 ) roland | klute mit physics annual 2010 gunther roland and Markus Klute ver the last few decades, teams of physicists and engineers O all over the globe have worked on the components for one of the most complex machines ever built: the Large Hadron Collider (LHC) at the CERN laboratory in Geneva, Switzerland. Collaborations of thousands of scientists have assembled the giant particle detectors used to examine collisions of protons and nuclei at energies never before achieved in a labo- ratory. After initial tests proved successful in late 2009, the LHC physics program was launched in March 2010. Now the race is on to fulfill the LHC’s paradoxical mission: to complete the Stan- dard Model of particle physics by detecting its last missing piece, the Higgs boson, and to discover the building blocks of a more complete theory of nature to finally replace the Standard Model. The MIT team working on the Compact Muon Solenoid (CMS) experiment at the LHC stands at the forefront of this new era of particle and nuclear physics. The High Energy Frontier Our current understanding of the fundamental interactions of nature is encap- sulated in the Standard Model of particle physics. In this theory, the multitude of subatomic particles is explained in terms of just two kinds of basic building blocks: quarks, which form protons and neutrons, and leptons, including the electron and its heavier cousins. From the three basic interactions described by the Standard Model—the strong, electroweak and gravitational forces—arise much of our understanding of the world around us, from the formation of matter in the early universe, to the energy production in the Sun, and the stability of atoms and mit physics annual 2010 roland | klute ( 41 figure 1 A photograph of the interior, central molecules.
    [Show full text]
  • What Is Next for the Lhc?
    Building new technologies Fuelling industry Particle accelerators, like those at the heart of the and economy LHC, are now being adopted for cancer therapies using WHAT IS NEXT protons which, unlike current therapies, deposit all their energy in the same place, making them ideal for treating FOR THE LHC? STFC funds the UK membership to CERN, which gives tumours near to delicate organs. UK scientists and engineers access to the vast amount of data and research that takes place. New technology and systems are still being developed around the LHC, allowing us to ask new questions and Since the LHC became operational, UK industry make exciting discoveries and progress in a range of has won valuable contracts at CERN worth different fields. £102 million (2010-2015). Of these, £15 million were awarded in 2015. Inspiring the next generation Engineering success This exciting science is prompting more young people to consider careers in physics and engineering, fields that Many engineering disciplines were involved in the are highly prized throughout the UK economy (during design, construction and maintenance of the LHC. the academic year that the Higgs boson was discovered, More than 1,600 superconducting magnets were British universities received 2,000 more applications for installed, with most weighing in excess of 27 tonnes, physics degrees than in previous years). in a collaborative effort involving more than 10,000 scientists and engineers from over 100 countries. CERN provides opportunities for both apprentices and graduates to visit and work at the site, so more Universities across the UK helped build the highly young people have the chance to build the career that sensitive detectors at the heart of the LHC’s they want.
    [Show full text]